7.5 Files

File is must-have object in every single computer device, and web applications also have many usage with files. In this section, we're going to learn how to operate files in Go.

Directories

Most of functions of file operations is in package os, here are some functions about directories:

func Mkdir(name string, perm FileMode) error

Create directory with name, perm is permission, like 0777.
func MkdirAll(path string, perm FileMode) error

Create multiple directories according to path, like astaxie/test1/test2.
func Remove(name string) error

Remove directory with name, it returns error if it's not directory or not empty.
func RemoveAll(path string) error

Remove multiple directories according to path, it will not be deleted if path is a single path.

Code sample:

package main

import (
	"fmt"
	"os"
)

func main() {
	os.Mkdir("astaxie", 0777)
	os.MkdirAll("astaxie/test1/test2", 0777)
	err := os.Remove("astaxie")
	if err != nil {
		fmt.Println(err)
	}
	os.RemoveAll("astaxie")
}

Files

Create and open files

Two functions to create files:

func Create(name string) (file *File, err Error)

Create file with name and return a file object with permission 0666 and read-writable.
func NewFile(fd uintptr, name string) *File

Create file and return a file object.

Two functions to open files:

func Open(name string) (file *File, err Error)

Open file with name with read-only permission, it calls OpenFile underlying.
func OpenFile(name string, flag int, perm uint32) (file *File, err Error)

Open file with name, flag is open mode like read-only, read-write, perm is permission.

Write files

Functions for writing files:

func (file *File) Write(b []byte) (n int, err Error)

Write byte type content to file.
func (file *File) WriteAt(b []byte, off int64) (n int, err Error)

Write byte type content to certain position of file.
func (file *File) WriteString(s string) (ret int, err Error)

Write string to file.

Code sample:

package main

import (
	"fmt"
	"os"
)

func main() {
	userFile := "astaxie.txt"
	fout, err := os.Create(userFile)		
	if err != nil {
		fmt.Println(userFile, err)
		return
	}
	defer fout.Close()
	for i := 0; i < 10; i++ {
		fout.WriteString("Just a test!\r\n")
		fout.Write([]byte("Just a test!\r\n"))
	}
}

Read files

Functions for reading files:

func (file *File) Read(b []byte) (n int, err Error)

Read data to b.
func (file *File) ReadAt(b []byte, off int64) (n int, err Error)

Read data from position off to b.

Code sample:

package main

import (
	"fmt"
	"os"
)

func main() {
	userFile := "asatxie.txt"
	fl, err := os.Open(userFile)		
	if err != nil {
		fmt.Println(userFile, err)
		return
	}
	defer fl.Close()
	buf := make([]byte, 1024)
	for {
		n, _ := fl.Read(buf)
		if 0 == n {
			break
		}
		os.Stdout.Write(buf[:n])
	}
}

Delete files

Go uses same function for removing files and directories:

func Remove(name string) Error

Remove file or directory with name.( name ends with / means directory )

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7.5 Files

Directories

Files

Create and open files

Write files

Read files

Delete files

Links

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